Obj. 1: Extend the N replacement approach to soft white winter wheat for guiding precision management of fertilizer N and crop residue to optimize soil microbial processes and maximize the biological potential of soil. 1A: Evaluate grain protein concentration and yield response to N under varying levels of water to define the critical protein level and fertilizer N equivalent to a unit change in protein for popular cultivars of soft white winter wheat. 1B: Determine whether uniformity of protein levels in the crop can be achieved with the precision N replacement approach. 1C: Adapt instruments and algorithms to support on-farm implementation of the N replacement approach to precision fertilizer management in dryland wheat production systems. 1D: Evaluate the effects of residue management (standing, distributed on the soil surface, or removed) on the plant-available N, precipitation capture efficiency, crop productivity, weed density, and microbial activity during the 13 months of fallow. Obj. 2: Identify whether soil microbial communities adapted to dry environments benefit plant fitness under water limited conditions. 2A: Identify the composition of microbial consortia naturally adapted to low water availability. 2B: Determine whether cultivar selection and N management can be manipulated to shift the structure and function of microbial communities to benefit plants under water stress. Obj. 3. Develop resilient cropping systems and strategies that increase resilience, improve economic returns, and enhance ecosystem services; assess their economic and environmental performance of various cropping systems in concert with their supporting components; and develop decision support systems for optimizing agronomic production in these cropping systems. 3A: Compare economic returns from the variable N replacement approach based on previous season’s site-specific SWW crop yield data and conventional uniform N placement based on field bulk soil sampling and laboratory testing. 3B: Increase dryland farming resilience by developing cropping systems more intensive and diverse than the conventional winter wheat-fallow system. 3C: Investigate the yields and economic returns of alternative crops following winter wheat and winter wheat following cover crops across low and intermediate precipitation zones using current and future climate scenarios. Obj. 4. Increase the sustainability resilience and tolerance of the dryland crop production system to biotic and abiotic stressors through improved understanding of developmental, environmental, and management factors that limit plant health and growth, including but not limited to stress tolerance, water use efficiency, and disease resistance. 4A: Evaluate stress indicators and yield components of wheat in alternative cropping systems compared to wheat-fallow with relation to soil water availability, disease incidence, and rotational crop morphology. 4B: Investigate crop response to water deficit, high temperature, and/or nitrogen availability.
1A: A winter wheat-fallow Cultivar-Fertility Study located at 2 sites in the low and intermediate precipitation zone in Eastern Oregon will include 3 soft white winter wheat cultivars fertilized with inorganic nitrogen (N) at 4 rates. The study will be repeated for 3 years. Yield and grain protein concentration (GPC) measured with near-infrared spectroscopy will define the critical GPC, an indicator of crop N deficiency or adequacy. 1B: A N-Replacement Study will follow 1A in which plots will be split and fertilized based on 1) amount of N needed to achieve target protein based on the critical GPC, and 2) university recommendations based on soil N and potential yield. Select plots will be analyzed for inorganic N, nutrient cycling capacity, microbial community composition, N leaching and gaseous N loss. 1C: The GPC measurements from the relatively inexpensive AvaSpec2048 spectrophotometer will be compared to data from dry combustion. Publicly available software will be adapted from Yield Editor software in collaboration with ARS, Columbia Missouri. 1D: Winter wheat residue in the 2 precipitation zones 1) cut high, left standing, 2) cut high, flattened, 3) cut low, spread, 4) cut low, removed. Measurements include yield, soil/air temperature, air movement, soil water content, inorganic N, and microbial nutrient-cycling activity. 2A: Rhizosphere and bulk soil microbial communities will be characterized from plots replicated in the low and intermediate precipitation zones. Soils will be analyzed for chemistry and enzymes related to carbon and N-cycling, and microbial composition. 2B: Rhizosphere soils collected from different cultivars of 1A at 2 N rates will be analyzed for nutrient cycling activity and communities sequenced from treatments promoting or inhibiting activity. Microbial communities will be evaluated for benefit to wheat in a microbial transfer potting experiment. 3: Economic benefit from replacement N management and intensified cropping systems will be evaluated. An alternative crop trial (AC) and cover crop trial (CC) will be conducted. The winter wheat (WW)-chemical fallow (CF) system will be intensified in a low precipitation (<250 mm) site as a WW-AC-CF rotation and at a high precipitation (<420-mm) site as a WW-AC rotation. The CC trial will be conducted at both sites as WW-cover crop fallow. Each trial will be initiated at a new location for three replicate years. A calibrated model will be provided within a crop simulation platform that will be useful for determining the different alternative crops and cover crops that producers are likely to consider. 4: The plant stress response and yield differences will be evaluated in the alternative and cover crop trials. Soil water availability, disease incidence, soil nutrient cycling, soil chemistry and yield traits will be quantified in each of the trials. Multiple regressions will be used to model the yield and stress variables as a function of the abiotic stressors. Results will identify benefits or detriments of alternative cropping systems to the primary wheat crop in terms of herbicide use, disease incidence, nutrient availability, soil quality, and water availability.
In support of Objective 1, significant progress was made to define the critical grain protein level for soft white winter wheat and determine how applied nitrogen (N) influences microbial communities relevant to nitrogen cycling. The N equivalent to a unit change in protein was identified for four popular cultivars in the region. A region-specific algorithm based on the slope of the relationship between applied N and protein was derived to help farmers target a desired grain protein level in the next season’s crop. For Sub-objective 1A, the Year 2 cultivar-fertility trial was successfully harvested, and the Year 3 trial was planted. The first nitrogen-replacement trial of Sub-objective 1B was seeded in fall 2022. Challenges encountered at seeding due to new equipment and inexperience resulted in overfertilization of the trial rendering the experiment ineffective for targeting low grain protein. Although the trial will not determine whether uniformity of protein levels can be achieved with precision N placement, the results can be used to further optimize the method with protein levels obtained in a year when both N and annual precipitation were highly available for plant growth. Under Sub-objective 1B, we made significant progress analyzing measurements of nitrogen in the grain of winter wheat, nitrogen lost to the atmosphere, and nitrogen lost below the soil profile. Fertilizer use efficiency was computed for each year of the three-year experiment. Significant progress was made on Sub-objective 1C in evaluating a grain yield/protein mapping software for growers who are interested in computing tools that make use of grain yield and protein maps to create fertilizer application plans. A live video listening session was organized that provided producers from Missouri and Oregon with an opportunity to view and assess the function of a software prototype. Resulting feedback was used to improve functional components of the software. Methods to prepare the software for final packaging and release are being evaluated. Progress was made on the residue height experiment of Sub-objective 1D. Winter wheat was successfully cultivated following fallow with different residue treatments at both the low and high precipitation sites. The second trial for the study was initiated by implementation of the residue treatments and instrumentation for measurement of soil water, soil temperature, near-surface soil temperature, relative humidity, and wind speed. The second trial will be planted to winter wheat in the fall for the final yield measurement of the experiment. In support of Objective 2, significant progress was made in the collection and analysis of root-impacted soils at both the low and high precipitation regions. The study was expanded to analyze soil communities throughout the wheat-fallow rotation with timepoints of early growth (tillering), post-harvest fallow, mid-fallow (spring), and late-fallow (pre-plant) for two complete years. Significant progress was made on the development of a robot-assisted, microplate protocol that couples the analysis of anaerobic mineralization to soil nitrate, nitrite, and ammonia. In brief, a liquid handling robot will perform the transfer of soil extracts to a microplate followed by reagents for a nitroprusside-based analysis of ammonium, Griess reagents for nitrite, and Griess reagents plus vanadium for nitrate. For Sub-objectives 2A and 2B, collected soils have been analyzed for ammonia oxidation and amidase activity, and a subset analyzed for total C, N, and pH. Progress was also made on Sub-objective 2A by extraction of DNA from root-impacted soils collected during tillering at both sites and for two crop years. Additionally, progress was made in evaluating the effects of nitrogen management on the soil community composition and nutrient cycling capacity in the long-term plots in Pendleton managed under wheat-fallow with no fertilizer, urea-ammonium-nitrate or manure. Under Objective 3, progress was made on data collection. Due to challenges in Objective 1 for the N-replacement trial, production outputs for the first year analysis are not available. Significant progress was made on Sub-objectives 3B and 3C through a cooperative agreement. The alternative crop and cover crop trials at the low- and intermediate-precipitation sites were successful in generating data for plant biomass, soil water availability, weed pressure, and yield. Yield data and biomass production were evaluated and will inform the development of a Phase II trial. Datasets of weather, crop yields, soil water-related attributes and management inputs have been generated. Progress was made on Objective 4 with the analysis of wheat biomass from three different trials. For Sub-objective 4A, plants were collected from the alternative crop and cover crop trials when wheat was at physiological maturity to compare yield formation between cropping systems. This milestone was expanded to evaluate the belowground microbial factors of bacterial and fungal communities as well as soilborne pathogens following cover crops. Regarding Sub-objective 4B, progress was made on the evaluation of wheat for nitrogen assimilation, physiological indicators of stress and yield components. Supply chain issues constrained equipment procurement and negatively impacted our ability to assess transpiration and chlorophyll fluorescence as physiological indicators of stress. Sub-objective 4B was also expanded to include novel research on the nutritional quality of regional wheat in terms of mineral element densities in grain. Substantial process has been made on sample processing and data analysis, and initial progress has been made on interpretation of the results.
1. Dryland wheat-fallow systems are more profitable than intensified rotations with oilseeds in low rainfall areas. With demand for renewable diesel and jet fuel expected to increase in the future, there is need to produce bio-feedstocks that will help the trucking and aviation industries decarbonize and reduce reliance on petroleum. ARS scientists in Pendleton, Oregon, examined profit opportunities for producing Brassica oilseed crops in rotation with winter wheat under low rainfall (less than 12 inches) in eastern Oregon. Yields of winter wheat increased and were more economically competitive after fallowing with conservation (minimum) tillage versus fallowing with conventional intensive tillage. Due to relatively low oilseed yields, three-year rotations of winter wheat-spring carinata (mustard)-fallow, winter napus (canola)-spring wheat-fallow, and spring carinata-spring wheat-fallow under conservation tillage experienced lower average profitability and greater income variability than conventional two-year rotations of winter wheat-fallow regardless of tillage intensity. Growers cannot be expected to cover total production costs at present market prices when winter canola or spring carinata are grown in low precipitation areas. Oilseed prices must double to approach the total net return of winter wheat-fallow under intensive tillage.
2. Long-term fertilization imparts stable changes to soil nutrient cycling enzymes. Soil enzymes are critical to the soil’s ability to release and cycle nutrients from organic matter. Because farming practices, such as nitrogen management, can impact the soil microbial communities both directly and indirectly through changes to the soil environment, it is important to understand the effects of management on the soil chemistry and overall nutrient cycling capacity. ARS scientists in Pendleton, Oregon, and Pullman, Washington, evaluated enzymes important in carbon, nitrogen, phosphorus, and sulfur supply in soils managed under wheat-fallow cultivation since 1931 that received either no fertilization, urea-ammonium nitrate (UAN), or manure. Soils receiving manure had significantly greater soil carbon, more neutral soil pH, and generally greater enzyme levels than either unfertilized or UAN-fertilized plots (with exception of pH-sensitive acid phosphatase enzyme). Comparison to historical studies showed that the treatment trends in nutrient cycling activity were mostly stable across a 32-year span although the acidification of the unfertilized and UAN-fertilized plots was reflected by the acid phosphatase enzyme. Overall, growers can expect long-term manure application to buffer a decline in soil pH, slow the loss of soil carbon and stimulate enzymes important in the release of carbon, nitrogen, phosphorous and sulfur from organic matter in dryland wheat-fallow cropping systems.
3. Biocrusts stimulate subsurface nitrogen cycling activity. Biological soil crusts (biocrusts) occur naturally across many ecosystems worldwide including deserts, polar regions, and agricultural systems. Biocrusts form in the top millimeters and are often comprised of cyanobacteria, moss, algae, fungi and archaea. ARS researchers in Pendleton, Oregon, and University of Florida collaborators, evaluated the effects of native agricultural biocrusts on the soil moisture, nitrogen-cycling capacity, and microbiome composition in the upper root zone of a sandy soil citrus orchard in Florida. The soil beneath biocrusts, compared to bare soil, had increased soil moisture during the dry season; greater soil nitrogen during citrus growth stages of high nutrient demand; and activity and relative abundance of microbes involved in nitrogen cycling. This information may guide producers to conserve naturally forming biocrusts as tools to increase soil health and influence nitrogen availability in crop production.
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Reardon, C.L., Klein, A.M., Melle, C.J., Hagerty, C.H., Klarer, E.R., Machado, S., Paulitz, T.C., Pritchett, L., Schlatter, D.C., Wuest, S.B. 2022. Enzyme activities distinguish long-term fertilizer effects under different soil storage methods. Applied Soil Ecology. 177. Article 104518. https://doi.org/10.1016/j.apsoil.2022.104518.
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